Exhaled nitric oxide decreases after positive food-allergen challenge

Forty children aged 3 to 16 years undergoing an allergen-food challenge at two centres were prospectively recruited for this study. FeNO was assessed before and repeatedly after the food-challenge.Data were obtained from a total of 53 challenges (16 positive, 37 negative) and were compared between the two groups. Half of the patients with a positive food challenge exhibited clinical upper respiratory symptoms. The FeNO significantly decreased in 7 of 16 patients with a positive challenge test within 60 to 90 minutes after the first symptoms of an allergic reaction.Our results show a significant decrease in FeNO after a positive food challenge suggesting involvement of the lower airways despite absence of clinical and functional changes of lower airways. Prospective blinded studies are needed to confirm these results.The current prevalence of food allergy in childhood varies between 6-8% during the first 3 years of life [1]. Food challenges are the gold standard for the diagnosis, in particular when the patient's history and specific IgE test results do not correlate, as well as for follow-up assessment. Among other potential symptoms, lower respiratory symptoms can be elicited by a positive challenge; they constitute a major risk factor for severe life-threatening anaphylaxis. It has also been observed that up to 40% of children and adolescents with food allergy but without asthma have concomitant asymptomatic bronchial hyperreactivity (BHR) to methacholine, in general without lung function changes [2,3].There is in agreement with the observation that fractional exhaled nitric oxide (FeNO) reflects bronchial allergic inflammation, and the measurement of FeNO has been proposed as a diagnostic tool for asthma [4], both in adults and children [5]. In addition, FeNO is related to the degree of bronchial inflammation in asthma and provides a non-invasive measure to monitor the anti-inflammatory treatment of asthmatic patients [6]. However it is unknown, whether FeNO chan